Summer-time denitrification and nitrous oxide exchange in the intertidal zone of the Yangtze Estuary

Sediment denitrification rates and nitrous oxide (N2O) exchange fluxes in the Yangtze estuary intertidal zone (mudflats and salt marshes) were measured in summer-time using an acetylene inhibition technique and an in situ static closed chamber method. N2O natural production rates ranged between 0.10 μmol N m−2 h−1 and 8.50 μmol N m−2 h−1, and the denitrification rates ranged from 18.71 μmol N m−2 h−1 to 35.87 μmol N m−2 h−1. The N2O natural production rates in overlying water were low, with intertidal sediment being the source of overlying water N2O during the submerged period. Data analysis indicated that most sediment N2O was not derived from denitrification, but from several other nitrogen-cycling processes. During the low tide, the middle tidal marsh was the source of atmosphere N2O (exchange fluxes changed between −11.03 μmol N m−2 h−1 and 13.17 μmol N m−2 h−1). 5 cm and 10 cm depth ground temperatures were significant factors controlling the emission flux. At the low tidal flat, N2O emission flux rates ranged from −5.75 μmol N m−2 h−1 to 0.49 μmol N m−2 h−1 at the sediment-atmosphere interface. Overall, the middle tidal marsh was the source of atmospheric N2O, while the low tidal flat was a sink for atmospheric N2O. Plants of the intertidal zone (Scirpus mariqueter and benthic algae) were significant factors controlling N2O exchange flux. Photosynthesis of intertidal zone plants inhibited the emission of N2O and induced consumption, while plant respiration may enhance N2O emission from the intertidal zone. N2O emission and consumption at the intertidal zone-atmosphere interface correlated positively with the emission and consumption of CO2.